An aircraft can include one or more fluid lines, e.g., tubing through which an aircraft fluid, e.g., fuel or other aircraft fluid, is transported. In some situations, a fluid line can be an inner tube used to transmit fluid. The inner tube can be surrounded by an outer tube (often referred to as a “sock”) to contain fluid in the event that the inner tube leaks, and to direct the leaked fluid to a collection point or separate chamber where it can be safely discharged. In such situations, the outer tube serves as a secondary containment mechanism that directs leaked fluid away from a source of the leak. The outer tube prevents leaked fluid from leaking into the fuselage or onto aircraft components, as the fluid could pose a safety hazard or damage the components or both. The length, weight and material of the inner and/or outer tube can limit an arrangement of the fluid transmission line in the aircraft. For example, if the inner tube and the outer tube have a long length, one or both of the tubes can sometimes sag under the weight of the tubes. Using shorter, more frequent lines to prevent sag only adds additional weight to the tubing system.